Aldol Condensation of 5-Hydroxymethylfurfural to Fuel Precursor over Novel Aluminum Exchanged-DTP@ZIF-8

Aldol condensation of 5-hydroxymethylfurfural (HMF) with acetone provides a route to upgrading of biomass intermediates into value-added compounds such as fuel precursors. This reaction gives C9 and C15 aldol adducts. These adducts can be further converted to jet fuel additives on hydrogenation and hydrodeoxygenation. Herein, we report a novel catalyst, namely, aluminum-exchanged heteropolyacid encapsulated inside the cage of ZIF-8 (Al-0.66-DTP@ZIF-8) (DTP = dodecatungstophosphoric acid; ZIF = zeolitic imidazolate framework) for selective synthesis of C9 adducts. The acidic nature of the catalyst gives a maximum conversion of HMF (99%) in 10 h, and the smaller pore diameter of ZIF-8 leads to the highly selective formation of C9 adducts (84.11%). The fresh and spent catalysts were characterized by various techniques. A kinetic model was developed, and the apparent activation energy for both monomer and dimer formations was calculated. Recyclability of catalyst was studied up to four cycles, and the catalyst was observed to be stable and reusable.